The Call of Everest Page 15

  The first response to lowered oxygen levels occurs almost immediately. Breathing speeds up so that the amount of air inhaled increases. This boosts the average oxygen levels in the lungs and subsequently in the blood. Heart rate also rises, which pushes more blood into the body and boosts the delivery of oxygen to the body’s tissues. In addition, soon after a person reaches high altitude, urine production increases, and some fluid may shift from within blood vessels to outside. This reduces the water in the bloodstream and makes the red blood cells more concentrated. That in turn increases the amount of oxygen transported for a given volume of blood. The reduction of liquid in the bloodstream, however, results in a drop in the volume pumped per beat of the heart. (A side effect of this process is dehydration, which can increase the likelihood of acute mountain sickness, or AMS, characterized by headache, nausea, and fatigue. Thus drinking large amounts of water is essential at high altitudes.)

  The hemoglobin molecule in red blood cells works differently depending on many factors: pH level, carbon dioxide level, temperature of the blood, for example. These properties of hemoglobin play an important part in how the body adapts to high altitudes. For example, as breathing increases at high altitude, the amount of carbon dioxide in the blood falls, reaching as low as one quarter of normal values by the time the climber reaches the summit of Everest. This causes blood to become more alkaline (making the pH level higher) and changes hemoglobin’s ability to bind oxygen molecules. This enables red blood cells at a high altitude to attract and bind oxygen better, despite the lower oxygen pressure in the lungs. The same factors can also influence the release of oxygen to tissues.

  Other responses to low oxygen levels include a constriction of blood vessels within the lungs, which raises the pressure levels in the lungs and on the right side of the heart. This effect can be almost immediate, but the level may continue to rise over time and with higher altitudes. Although high blood pressure in the lungs can have negative consequences over a long period of time, in the short term it may redistribute blood to more regions of the lungs, increasing the total surface area for the transfer of gases and moving oxygen into the bloodstream and carbon dioxide out to the lungs.

  LONGER-TERM ADAPTATION

  As the “stress” of high altitude continues, the body’s many low-oxygen-sensing genes, proteins, and cells regulate how the body adapts. The stimulation of one of these proteins (called hypoxia inducible factor 1 alpha, or HIF-1 a) sets off a cascade of changes throughout the body, including the stimulation of a hormone (erythropoietin) that controls red blood cell production. This then increases the blood’s carrying capacity of oxygen.

  STONE MONUMENTS, OR chortens, at the mountain pass of Thukla on the way to Base Camp honor climbers and Sherpas who have died on Everest. Covered in prayer flags, the memorials stand as a sobering reminder that not everyone makes it back from the mountain.

  Other longer-term changes include the increased ability of the kidneys to excrete bicarbonate, which buffers against swings of pH levels in the blood. This critical adaptation lowers the pH level of the blood and allows the gradual ramping up of breathing to higher and higher levels over several weeks at altitude. In addition, there is an increase in oxygen-carrying proteins in muscle called myoglobin—a relative of hemoglobin. The ratio of capillaries (branching blood vessels) to muscle fibers may increase and improve ability to supply oxygen to muscle. (Muscles are made up of many smaller fibers.) Many climbers experience a rapid loss of weight and muscle at extreme altitude. (The melting away of muscle without a change in the number of capillaries may explain the increased capillary-to-fiber ratios.)

  VOICES

  OVERNIGHT ON EVEREST

  I suppose I had it coming to me. I was the victim of my own ambition, my own weakness, the cold, the altitude … I paid the price for pushing on late in the day. There were moments that afternoon when I thought I had realized my worst terror—driving myself to the top of the world then finding I had no reserves left to get back down. After one frantic, blind glissade down the steep flank of the South Summit, I collapsed in a wild, gasping, fish-out-of-water panic, dug a hole in the snow, and just sat shivering violently, feeling very sorry for myself.

  But it was a precarious perch, and I knew I had to get a grip and stop being a victim. At dusk I climbed down to an easier section of the ridge. As darkness enclosed the mountain I switched on my headlamp and struggled to make sense of half-remembered rocks I had passed on the way up, ten hours earlier. (Not knowing the correct normal route we had climbed a steeper, more direct line, gaining the Southeast Ridge some way above “The Balcony.”) In the end I decided it would be safer to wait for the dawn. So I settled down for the long shiver.

  At first I sat on a rock. Rocks are warmer—I knew that. But this one sloped and I longed, no we longed—my imaginary older companion and I—to lie down flat. And I knew anyway that it’s better for your circulation if you stretch your legs horizontally. So we got up and started digging; but we were so tired, so feeble, so desperate to lie down, that we only managed a five-foot-long ledge in the snow before settling down with knees bent out over the Kangshung Face.

  By now it must have been dark for at least an hour and I still had seven hours incarceration before the release of daylight. I later calculated the altitude at about 8,550 metres above sea level. Night temperature in May: somewhere between -30° and -40° centigrade. Chances of survival? Well, actually, not too bad. The afternoon blizzard had subsided and the air was still …

  Although I never planned, or wanted, to bivouac on Everest, the grim possibility had always been lurking there, unspoken. I had thought very carefully about all my layers of clothing. And I now I took care to pad hips and head with spare mittens—token wads of extra insulation between my bones and the insidious creeping cold. I also plunged my long ice axe into the snow as a fence post to stop me rolling over during the night.

  There is a myth that if you fall asleep in these situations you never wake up … I think at one point I did actually slumber for a while, and I didn’t die. Mostly though I was in semi-conscious limbo, drifting through a fog of half-rational associations … Occasionally my rational consciousness would jolt me awake and banish the phantoms. I forced myself to chew some almond Hershey bar—must be some calories there. I sucked the last semi-frozen trickle from my water bottle. I thought about removing crampons and boots to massage wooden toes, but decided it was too risky—better to concentrate on looking after my hands. And I shivered. But it didn’t really feel any worse than my worst alpine winter bivouacs 14,000 feet lower: I was anaesthetised by altitude. And in any case, I was no longer a victim: I was just waiting patiently for the dawn.

  —STEPHEN VENABLES In 1988 mountaineer, writer, and inspirational speaker Stephen Venables became the first Briton to summit Mount Everest without supplementary oxygen.

  HOW HIGH FOR HOW LONG?

  What are the true limits to high-altitude exposure? While many call the process preparing for an Everest summit “acclimation,” others would say the body gets better at “tolerating” the extremes of hypoxia (low oxygen). That tolerance continually remains at a delicate threshold, particularly at the elevations above Everest Base Camp. That’s why over the course of history, few long-standing communities have survived at extreme altitudes. In fact, no permanent communities on the globe exist above 17,000 feet. (For comparison, Everest Base Camp is at about 17,500 feet.) Most of the communities even close to that altitude grew up around industry (mining towns, railway communities, or observatories) and struggle with ongoing problems related to the extreme altitude. The highest permanent mining community is La Rinconada in southern Peru, which extends from altitudes of 4,900 to 5,200 meters (16,000 to 17,000 feet). In Tibet several villages are located at similar elevations, but most settlements are near or below 15,000 feet, which seems to be a threshold for maintaining health and reproduction. Even the highest Sherpa villages are lower than 15,000 feet, or 4,600 meters, high. (Dingboche is at 4,400 meters an
d Pheriche 4,240 meters.)

  The Tibetan and Andean people who live in the highest plateau regions of the world provide an interesting comparison of how humans can adapt to extreme elevations. Although we do not know how long each of these groups has lived at high altitude, the consensus is that the Tibetans settled their plateau communities first and thus have had a greater chance for natural selection and adaptation to high altitudes. Both populations have adapted to their environment and appear to have relatively normal energy expenditures at rest and relatively adequate exercise capacities, even at altitudes up to about 4,000 meters. This contrasts greatly with most healthy adults living at sea level, whose exercise capacity falls by 20 to 30 percent at these altitudes. Although exercise tolerance can increase over time at high altitude, the Tibetan and Andean inhabitants show relatively comprehensive adaptation to high altitudes.

  The two groups may have achieved this acclimatization by different means, however. For example, the Tibetans appear to breathe more than the Andeans and have more blood flow through the lungs, despite lower average hemoglobin levels and oxygen saturation values. The Tibetans appear less susceptible than Andeans to two conditions associated with living at high altitudes: chronic mountain sickness (CMS), in which the number of red blood cells increases to the point where the blood gets sludgy and difficult for the heart to pump it throughout the body, and high blood pressure in the lungs, a risk factor for CMS. Lack of oxygen may contribute over time to the selection of genes that help the acclimation process. Scientists do not know whether the Tibetans’ apparently more complete adaptation is due to the number of generations they have lived at high altitude. Discovering the genetic basis for these adaptations may help find better ways to help the body tolerate low oxygen levels—important for many patients—or may help identify those who will either do well or face high risk at high altitudes.

  1963 CLIMBER BARRY Bishop permanently lost toes during the historic climb. Rates of frostbite have been reduced over the years thanks to improvements in equipment.

  SUPPLEMENTAL OXYGEN

  The use of oxygen on Mount Everest remains controversial. For years many thought that climbers could not survive without supplemental oxygen, but eventually Reinhold Messner and Peter Habeler proved otherwise in 1978. Of the more than 3,500 people to reach the summit of Everest, roughly 5 percent have done so without oxygen. Still, a climber is almost two times more likely to die while summiting Everest without using oxygen.

  Dr. Thomas Hornbein, a member of the original U.S. expedition to summit Everest in 1963, estimated the influence of supplemental oxygen. Mayo Clinic researchers recently modeled these results using data from the 2012 expedition and a simulated ascent of Everest that took place in 1985. In that study, a team of 27 investigators “climbed” for 40 days as if to the summit in an altitude chamber. Results show that a climber using supplemental oxygen will have a hypoxic stress level at the summit that is lower than the one experienced at Base Camp at rest without oxygen. With oxygen, a climber at Camp IV trying to sleep actually maintained oxygen saturation levels in the mid to upper 90s, close to sea-level values. Thus supplemental oxygen makes a big difference, although some might say that six weeks of acclimating to extreme hypoxia results in muscles less able to use the oxygen being delivered.

  MARK JENKINS LEARNS to use an oxygen mask system. At Base Camp there is only half the oxygen available that there is at sea level; on the summit, 33 percent. Five percent of people who have summited Everest have done so without supplemental oxygen.

  THE ULTIMATE LABORATORY

  Attempting to mimic extreme conditions in the laboratory is difficult, if not impossible. The field is the ultimate laboratory where human physiology and environment come together. Few atmospheric chambers can mimic true high-altitude conditions, complete with unpredictable temperature fluctuations and humidity levels as well as human factors such as dehydration, physical activity, and psychological stress. Field work on Everest complements the highly controlled laboratory conditions. The less predictable conditions in the field can lead to observations and findings that had not been considered or explored.

  2012 STUDIES AND BEYOND

  Fifty years after the first American ascent of Everest, the names and faces have changed but the challenge of the climb and the passion for unlocking the scientific secrets of high-altitude physiology remain alive and well. Fifty years ago, the climbing “team” consisted of 19 members, including five with master’s degrees, five with Ph.D.’s, three medical doctors, and a group of experienced climbers and their support staff. For the studies of the medical aspects of high-altitude exposure, primarily cognitive and psychological measures, the study subjects were essentially members of the team. Support then as now was an ongoing challenge, but the National Geographic Society, National Science Foundation, U.S. Air Force, Office of Naval Research, the State Department’s Bureau of Educational Exchange and Cultural Affairs, the U.S. Army Quartermaster Corps, and NASA all provided significant funding for the 1963 climb.

  This year’s team consisted of a similar number of individuals, along with multiple funding sources, including substantial support from the National Geographic Society and The North Face company. Team members included Ph.D. physiologists and geologists, physicians with expertise in critical care and flight medicine (USAF), a research associate, carefully selected North Face and National Geographic athletes, athlete-photographers, videographers, bloggers, product-innovation experts with The North Face company, and a National Outdoor Leadership School senior field instructor.

  THE HIGH-REACHING GOALS

  The North Face company develops products based on feedback from the top athletes around the world, people who push the envelope on human performance in extreme and unlikely environments. This focus on human performance in extreme environments like Everest became the impetus for the North Face-Mayo Clinic relationship, since the Mayo Clinic also has an extensive history of such studies. Mayo researchers played a critical role in the early understanding of flight physiology and health countermeasures for pilots. While researchers can learn a lot from studying chronic disease (one end of the health spectrum), our belief is that there is also much to be learned from studying the exceedingly fit athletes who push the other end of the health spectrum.

  ELITE CLIMBER EMILY Harrington, a member of the 2012 North Face/National Geographic expedition team, takes a lung-capacity test. Part of the team’s mission was to study the limits of performance at high elevation.

  The Mayo Clinic researchers had several goals for the 2012 Everest expedition. One was to better understand the limits of human performance at extreme altitudes. They also wanted to determine the relationship between altered sleep physiology (amount of REM sleep and/or the decrease in blood-oxygen levels at night) and altitude illness. They studied lung-fluid regulation and muscle loss, and they collaborated to evaluate the impact of equipment and clothing on sleep physiology and performance in athletes. The studies on oxygen deprivation complemented ongoing clinical studies at the Mayo Clinic with patients. Climbers wore devices that were light and unobtrusive even during difficult ascents, which allowed the continuous monitoring of participants 24 hours a day and gave us a more dynamic and comprehensive view of the body under extreme conditions. Researchers collected an estimated 27 billion data points over the course of the expedition.

  WHAT WE LEARNED

  It is fascinating to realize how much what we learned about adaptive physiology in extreme altitudes applies to the treatment of several chronic diseases. In particular, our laboratory has been interested in patients who suffer from chronic heart failure, a condition in which the pumping action of the heart is less than ideal.

  The American Heart Association estimates that in 2010, some six million patients in the United States experienced heart failure, at a cost of nearly $40 billion. Roughly 700,000 new cases are diagnosed annually. Heart failure is the most common diagnosis in Medicare beneficiaries, and these types of patients have very high admission
and readmission rates. The causes of this complex condition are cumulative and broad in origin (e.g., high blood pressure, heart attack, sleep apnea, alcohol, viruses). Many of the current treatments and medications target the body’s response to heart failure rather than having a direct therapeutic influence on the heart.

  The parallels of heart failure and high-altitude extremes are therefore interesting. A quote from National Geographic field staff writer Mark Jenkins describes what it feels like to climb at extreme altitudes: “Duct-tape two bricks to the bottom of each foot, put a straw in your mouth, and then charge up several flights of stairs—breathing only through the straw, of course. If you find you’re sucking wind like a race horse, nostrils flaring, mouth drooling, and your heart is jackhammering in your chest, and your legs are as heavy as bags of concrete—welcome to high altitude.” The most common symptoms at high altitudes include shortness of breath with exertion, extreme fatigue, trouble sleeping and difficulty breathing, weakness and malaise, peripheral edema, lung congestion, headache, nausea, and dizziness or light-headedness—many of the same symptoms that bring heart-failure patients to their local physician.

  As a climber reaches high altitude, a small, complex organ called the carotid body—located near the neck area—senses the change in oxygen in the blood and tells the brain to immediately increase breathing. The carotid body also stimulates the nervous system, like a stress response. That sets off a number of processes within the body, such as an increase in nervous system activity and release of mediators such as adrenaline. Recent tests have shown that the reduction in blood flow after heart failure—caused by a drop in the heart’s pumping action—stimulates a response in the carotid body that is similar to what occurs at high altitude, when it senses low blood flow as hypoxia. The similarities also extend to the carotid body’s stimulating overbreathing in heart-failure patients and stimulating the nervous system as a stress response.